1. Field of the Invention
The present invention relates to a photographing lens unit for a stereoscopic or “3-D” photographing lens unit, a photographing apparatus, and a photographing lens system.
2. Description of the Related Art
FIG. 6 shows the configuration of a stereoscopic photographing lens unit according to a conventional example. The basic configuration of a stereoscopic photographing and recording apparatus will be explained with reference to FIG. 6. The stereoscopic photographing and recording apparatus employs a field time sharing method, and is based on an interlaced video system as in the NTSC. Specifically, images equivalent to those viewed by one eye and images equivalent to those viewed by the other eye are sorted into odd fields and even fields.
Referring to FIG. 6, an optical system is separated into right and left sections at the end adjacent to an object, and adapted to admit a right beam or a left beam of light, respectively, by the function of liquid crystal shutters 81R and 81L disposed on the right and left sides, respectively.
The beams of light are merged into a single beam of light by mirrors 82R, 82L, and 83, and pass through a stop 84 so as to be formed into an image at an image pick-up device 88 through lenses 85, 86, and 87. At a given timing, only one of the right and left beam of light reaches an imaging surface.
A picture signal obtained by photoelectrically converting the beam of light formed into an image on the imaging surface as described above is recorded onto a recording medium.
Among several different types of information involved in stereoscopic photography, there are some types of information required to view a stereoscopic image properly at the stage of display.
The information required for the above stereoscopic photographing includes:
(1) Angles of view of an image (vertical and horizontal),
(2) Length of base line: Distance between the points corresponding to right and left eyes, respectively (pupil distance),
(3) Angle of convergence: Inward angles (in degrees) of the optical axes of the right and left eyes,
(4) Whether the odd/even of a field corresponds to left/right or right/left, and
(5) Distance to a subject (Value measured by a ranging system, such as an AF system).
Supplementary information includes:
(6) Information regarding an aperture, and
(7) Shutter speed.
The various types of information mentioned above are distributed among an optical unit (lens unit) and a photographing unit (the main unit of a camera) as follows:
(1) Optical unit is responsible for information regarding:                (a) Focal length,        (b) Length of base line,        (c) Angle of convergence, and        (d) Distance to a subject (AF system).        
(2) Photographing unit is responsible for information regarding:                (a) Size of a photographing area of an image pickup device, such as a CCD,        (b) Photoelectric conversion cumulating timing of an image pick-up device, such as a CCD (Time of lag from synchronizing signal), and        (c) Whether a field is an odd or even number.        
When viewing a stereoscopic image, in order to reproduce a further improved three-dimensional appearance thereof, it is desired to properly set the size of a display device and the distance from a viewer to the display device.
For instance, if a person who is 170 cm high is standing at a 3-meter distance, and the angle of view is set so that the person is exactly fitted from the top to bottom of a screen, and the angle of convergence is set to the person at the 3-meter distance, then a screen measuring 170 cm vertically should be disposed at a distance of three meters to directly reproduce and display a stereoscopic image in order to reproduce the image with fidelity.
The relationship between even/odd and left/right of a field is saved in the form of even/odd of the field of a recording picture signal. Hence, as long as the defined relationship in a photographing apparatus is known, right and left images can be correctly reproduced.
Furthermore, if the angle of view, parallax, the angle of convergence, etc. are known, then good images can be reproduced, depending on a display device or setting, such as a viewing distance, thereof.
The angle of view can be obtained by conversion based on the focal length of an optical system if the size of a photographing area of an image pick-up device (CCD) has been decided.
A proper set value for the distance between a display device and a viewer can be determined from the distance to a subject and the angle of view.
However, in the conventional photographing and recording apparatus described above, the above-mentioned information is not recorded onto a recording medium wherein images have been recorded, thus presenting a problem in that only the recording medium to which images have been merely recorded is handed to a third party, and good three dimensional images cannot always be reproduced if the images are viewed at an improper setting.
An incorrect left/right relationship, in particular, has resulted not only in the loss of a three-dimensional appearance but an awkward appearance of images also in some cases.